Feedstocks containing higher molecular weight hydrocarbons are cracked by contacting the feedstocks under elevated temperatures with a cracking catalyst whereby light and middle distillates are produced. Typically, the octane number of the light distillate (gasoline) is dependent upon the riser temperature, conversion level of operation or the catalyst type. Therefore, to increase the octane number of the gasoline, conversion of the hydrocarbon feed to lighter products must be increased by preferably raising the temperature of operation, or by increasing other operating variables such as catalyst to oil ratio. Unfortunately, a limit on the maximum operating temperature is set by reactor metallurgy, gas compressor constraint or other operating constraints. Increasing conversion by other means may also result in poor selectivity to desired products. The octane number of the gasoline may be increased by switching from a catalyst containing rare earth-exchanged Y zeolite to one containing ultrastable Y zeolite or ZSM-5, as is well known in prior art; however, such a switch will generally involve substantially higher costs, be time consuming, and above all, lead to significant reductions in the yield of gasoline.
Therefore, with the current national emphasis on lead-free gasoline, and the need for increasing gasoline octane number by means other than the addition of lead, it is desirable to have a modified cracking process available for increasing the octane number of the gasoline while minimizing the disadvantages associated with practices described in the prior art.
It is thus one object of the this invention to provide a regenerated cracking process, and a further object of this invention to provide a process for increasing the octane number of the gasoline from the process. Another object of this invention is to achieve the increase in octane number of the gasoline by modifying the method of introduction of feed to the riser reactor in a fluid catalytic cracking process.